Dual-profile steerable catheter with shaft support system for resisting axial compressive loads

ABSTRACT

A catheter includes a steering mechanism for manipulating the distal end of the catheter to obtain a plurality of deflection profiles, a torque transfer system to enhance torque transfer from the handle to the distal tip, and a support system to reduce undesirable deformation of the distal-end region during steering. The torque transfer system includes a flat ribbon within the relatively flexible distal-end region to enhance torque transfer through the distal-end region of the catheter. The support system includes a compression cage and longitudinal struts that are located within the distal-end region of the catheter. The support system can support axial loads and deflect laterally in the direction of the steering, thereby reducing the amount of stretching and compression of the catheter sheath within the deflecting region.

RELATED APPLICATIONS

[0001] This is a continuation of application Ser. No. 09/848,087, filedMay 2, 2001.

BACKGROUND OF THE INVENTION

[0002] The invention relates generally to catheters, and moreparticularly to a catheter having a steerable distal-end region with ashaft support system for resisting axial compressive loads.

[0003] The heart beat in a healthy human is controlled by the sinoatrialnode (“S-A node”) located in the wall of the right atrium. The S-A nodegenerates electrical signal potentials that are transmitted throughpathways of conductive heart tissue in the atrium to theatrioventricular node (“A-V node”) which in turn transmits theelectrical signals throughout the ventricle by means of the His andPurkinje conductive tissues. Improper growth of, or damage to, theconductive tissue in the heart can interfere with the passage of regularelectrical signals from the S-A and A-V nodes. Electrical signalirregularities resulting from such interference can disturb the normalrhythm of the heart and cause an abnormal rhythmic condition referred toas “cardiac arrhythmia.”

[0004] While there are different treatments for cardiac arrhythmia,including the application of anti-arrhythmia drugs, in many casesablation of the damaged tissue can restore the correct operation of theheart. Such ablation can be performed by percutaneous ablation, aprocedure in which a catheter is percutaneously introduced into thepatient and directed through an artery or vein to the atrium orventricle of the heart to perform single or multiple diagnostic,therapeutic, and/or surgical procedures. In such case, an ablationprocedure is used to destroy the tissue causing the arrhythmia in anattempt to remove the electrical signal irregularities or create aconductive tissue block to restore normal heart beat or at least animproved heart beat. Successful ablation of the conductive tissue at thearrhythmia initiation site usually terminates the arrhythmia or at leastmoderates the heart rhythm to acceptable levels. A widely acceptedtreatment for arrhythmia involves the application of RF energy to theconductive tissue.

[0005] In the case of atrial fibrillation (“AF”), a procedure publishedby Cox et al. and known as the “Maze procedure” involves continuousatrial incisions to prevent atrial reentry and to allow sinus impulsesto activate the entire myocardium. While this procedure has been foundto be successful, it involves an intensely invasive approach. It is moredesirable to accomplish the same result as the Maze procedure by use ofa less invasive approach, such as through the use of an appropriateelectrophysiological (“EP”) catheter system.

[0006] One such EP catheter system, as disclosed in U.S. Pat. Nos.6,059,778 and 6,096,036, includes a plurality of spaced apart bandelectrodes located at the distal end of the catheter and arranged in alinear array. The band electrodes are positioned proximal heart tissue.RF energy is applied through the electrodes to the heart tissue toproduce a series of long linear lesions similar to those produced by theMaze procedure. The catheters currently used for this procedure aretypically flexible at the distal end, and the profile at the distal endis adjustable. However, when using such catheters, it is often difficultto conform the distal-end profile to some of the irregular topographiesof the interior cavities of the heart. In other instances, it isdifficult for a multi-electrode catheter that is designed to producelong linear lesions to access and ablate tissue in regions that requireshort linear lesions, such as the so-called isthmus region that runsfrom the tricuspid annulus to the eustachian ridge. Ablation of tissuein this region, and other regions non-conducive to the placement ofmulti-electrode, long, linear-lesion ablation catheters within them, isbest accomplished by delivering RF energy to a tip electrode to producelocalized spot lesions or if longer lesions are required, by energizingthe tip while it is moved across the tissue.

[0007] Other catheters for producing spot lesions or tip-drag lesionstypically include a tip ablation electrode and a plurality of mappingband electrodes positioned at the distal end of the catheter. Thecatheters are steerable in that they are configured to allow the profileof the distal end of the catheter to be manipulated from a locationoutside the patient's body. Steerable catheters that produce multipledeflection profiles of their distal ends provide a broader range ofsteerability. However, known steerable catheters, such as that disclosedin U.S. Pat. No. 5,195,968, have steering tendons attached to a ribbonat or near the longitudinal centerline of the catheter. Because of therelatively short distance between the tendon attachment point and theribbon that resides along the centerline of the catheter sheath, a forceapplied to the tendon results in a relatively small bending moment fordeflecting the distal tip. The ribbon/tendon assembly is typicallyprovided clearance to allow the tendon to become substantially displacedfrom the centerline as deflection progresses, thereby enlarging themoment arm and consequently increasing the applied bending moment.Unfortunately, this requires such designs to include additional lumenspace, translating into larger catheter diameters. Larger diametercatheters are undesirable due to the increased trauma they inflict on apatient. Further, as the tendon displaces to the extent that it contactsthe catheter wall, the associated friction may necessitate greaterexertion to further deflect the distal tip. Lessening the amount offorce required to deflect the distal tip of a catheter by actionsoutside the catheter is desired in that the catheter tip can more easilybe deflected and placed in the correct location within a patient.

[0008] In some catheters that have a ribbon within the distal-end regionand a steering tendon affixed to the sheath at a point proximal thedistal tip within the distal-end region, undesirable deformation of thesheath can occur when the steering tendon is axially displaced in theproximal direction. More specifically, as the steering tendon is axiallydisplaced in the proximal direction, the portion of the sheath in thedistal-end region proximal the attachment point compresses, thus causingthe sheath to wrinkle, and the portion of the sheath distal theattachment point stretches. Such deformation of the sheath can lead tofluid ingress beneath the catheter's band electrodes or can cause damageto internal wires or mechanical components.

[0009] Hence, those skilled in the art have identified a need for atip-electrode, ablation catheter with a steerable distal-end region thatresists deformation even after repeated steering. The present inventionfulfills these needs and others.

SUMMARY OF THE INVENTION

[0010] Briefly, and in general terms, the present invention is directedto a catheter with a steerable distal-end region and a shaft supportsystem for resisting axial compressive loads.

[0011] In a first aspect, the invention relates to a catheter thatincludes a sheath having a proximal region, a distal-end region, and alongitudinal centerline. The catheter also includes at least onesteering tendon that is housed within the sheath. The at least onesteering tendon has a first end that is attached to the distal-endregion of the sheath, and a second end that is located at the proximalregion of the sheath. Movement of the at least one steering tendon in aproximal direction causes the sheath distal-end region to deflect. Thecatheter also includes a support system having a proximal end, a distalend and a lumen there between. The support system is sized to fit withinthe distal-end region of the sheath and is configured to deflectlaterally relative to the centerline and to resist axial compressionalong the centerline.

[0012] In a detailed aspect of the invention, the support systemincludes a helical coil that defines the lumen and at least one strutthat is secured to one side of the coil along the length of the coil. Inanother aspect, the support system includes a pair of struts secured todiametrically opposite sides of the coil. In a further aspect, thesupport system is formed of a resiliently deformable, shape-memorymaterial. In another detailed facet of the invention, the support systemincludes a linear array of hollow rings that defines the lumen, and atleast one strut that is secured to one side of each of the rings. In afurther facet, the support system includes a pair of struts that aresecured to diametrically opposite sides of each of the rings. In anotherdetailed aspect of the invention, the support system includes asubstantially tubular member with an array of notches. In a moredetailed aspect, the notches are diametrically opposite and offset fromeach other. In another detailed facet of the invention, the catheterincludes a ribbon isolation sleeve that has a proximal end attached tothe distal-end of the support system. In a further facet, the ribbonisolation sleeve is formed of a resiliently deformable material. In amore detailed facet the ribbon isolation sleeve includes a wire coilembedded within the material. In yet another detailed aspect of theinvention, the first end of the at least one steering tendon is attachedat a location offset from the centerline of the sheath.

[0013] In a second aspect, the invention relates to a catheter thatincludes a sheath having a proximal region and a distal-end region. Thecatheter also includes a first steering tendon that is housed within thesheath. The first steering tendon has a first end that is attached tothe distal-end region at a point proximate an inner surface of thesheath, and a second end that exits a proximal end of the sheath.Movement of the first steering tendon in a proximal direction causes thesheath distal-end region to deflect. The catheter also includes a secondsteering tendon that is housed within the sheath. The second steeringtendon has a first end and a second end. The first end of the secondsteering tendon is attached to the distal-end region at a pointproximate the inner surface of the sheath and proximal the attachmentpoint of the first steering tendon. The second end of the secondsteering tendon has a second end that exits the proximal end of thesheath. Movement of the second steering tendon in the proximal directioncauses the sheath distal-end region to deflect. The catheter alsoincludes a compression cage that has a proximal end, a distal end and alumen there between. The compression cage is sized to fit within thedistal-end region of the sheath and is configured to deflect laterallyand to support an axial load.

[0014] In a detailed aspect of the invention, the first end of thesecond steering tendon is coupled to the compression cage. In a moredetailed aspect, the first end of the second steering tendon attaches toa distal portion of the compression cage. In another detailed facet ofthe invention, the catheter also includes an anchor band that isattached to the distal end of the compression cage. In another facet,the first end of the second steering tendon is attached to the anchorband. In another detailed aspect of the invention, the catheter alsoincludes a torque transfer system that is housed within the compressioncage and is adapted to transfer torsional forces from the proximalregion of the sheath to the distal-end region of the sheath. In a moredetailed aspect, the torque transfer system includes an eyelet that issecured at the distal end of the proximal region of the sheath and theproximal end of the compression cage is secured to the eyelet. Inanother detailed aspect, the torque transfer system further includes aribbon that is housed within the compression cage and is configured todeflect therewith. The ribbon has a first end that is secured within theeyelet and a second end that is attached to the distal-end region of thesheath. In a further detailed aspect, the ribbon is positioned along thecenterline of the distal-end region of the sheath. In an additionalaspect, the ribbon is formed of a resiliently deformable, shape-memorymaterial. In a still further aspect, the ribbon has a substantiallyrectangular cross-section. In yet another aspect, the compression cageand the ribbon are each adapted to deflect in a direction, and thecompression cage further includes a ribbon locator that is adapted toalign the deflecting direction of the compression cage with thedeflecting direction of the ribbon.

[0015] In a third aspect, the invention relates to a catheter for usewith biological tissue that includes a sheath having a proximal regionand a distal-end region. The catheter also includes at least oneelectrode that is located in the distal-end region for transferringenergy to the biological tissue. The catheter further includes a firststeering tendon that is housed within the sheath. The first steeringtendon has a first end that is attached to the distal-end region at apoint proximate an inner surface of the sheath, and a second end thatexits a proximal end of the sheath. Movement of the first steeringtendon in a proximal direction causes the sheath distal-end region todeflect. The catheter also has a second steering tendon that is housedwithin the sheath. The second steering tendon has a first end and asecond end. The first end of the second steering tendon is attached tothe distal-end region at a point proximate the inner surface of thesheath and proximal the attachment point of the first steering tendon.The second end of the second steering tendon exits the proximal end ofthe sheath. Movement of the second steering tendon in the proximaldirection causes the sheath distal-end region to deflect. The catheteralso includes a compression cage that has a proximal end, a distal endand a lumen there between. The compression cage is sized to fit withinthe distal-end region of the sheath and is configured to deflectlaterally therewith and to resist axial compression. The catheterfurther includes a torque transfer system that is housed within thecompression cage and is adapted to transfer torsional forces from theproximal region of the sheath to the distal-end region of the sheath.

[0016] In a detailed aspect of the invention, the first steering tendonis secured within a distal tip of the sheath. In another aspect, the atleast one electrode includes a tip electrode that is located at thedistal end of the sheath, and the first steering tendon is securedwithin the tip electrode. In another detailed facet of the invention,the compression cage includes a helical coil that defines the lumen, andat least one strut that is secured to one side of the coil along thelength of the coil. In a more detailed facet, the catheter also includesan anchor band that has a proximal end and a distal end with a centrallumen there between. The anchor band is housed within the distal-endregion, and the proximal end of the anchor band is attached to thedistal end of the compression cage. In a further facet, the first end ofthe second steering tendon is attached to the anchor band.

[0017] These and other aspects and advantages of the invention willbecome apparent from the following detailed description and theaccompanying drawings, which illustrate by way of example the featuresof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a plan view with a broken-out section of a catheterconfigured in accordance with aspects of the invention and depictingcomponents of the catheter including a sheath, a steering mechanism anda steering handle;

[0019]FIG. 2 is a cross-section view of the construction of the proximalregion of the sheath taken along the line 2-2 from FIG. 1;

[0020]FIG. 3 is a cross-section view of the construction of thedistal-end region of the sheath taken along the line 3-3 from FIG. 1;

[0021]FIG. 4 is a cross-sectional plan view with a broken-out section ofthe distal portion of the catheter of FIG. 1 depicting detailedcomponents including steering tendons arranged to provide bidirectionalsteering profile capabilities, a torque transfer system, and a supportsystem;

[0022]FIG. 5 is a cross-sectional plan view of the distal-end region ofthe catheter of FIG. 1 depicting the attachment points for the steeringtendons, wherein the steering tendons are disposed approximately 180°apart and on opposite sides of the torque transfer system;

[0023]FIG. 6 is a tri-metric view with a broken-out section of thecatheter of FIG. 1 depicting the detailed components of the torquetransfer system including an eyelet, a flat ribbon and an anchor bandwith other items removed for clarity;

[0024]FIG. 7A is a view of a support system comprised of a flat-wirecoil and struts;

[0025]FIG. 7B is a view of a support system comprised of a round-wirecoil and struts;

[0026]FIG. 7C is a view of a support system comprised of a tubularmember with an array of deep notches;

[0027]FIG. 7D is a perspective view of the support system of FIG. 7C;

[0028]FIG. 7E is a view of a support system comprised of a linear arrayof hollow rings connected with struts;

[0029]FIG. 8 is a cross-section view of the distal-end region depictingthe steering tendons disposed approximately 180° apart and on oppositesides of the torque transfer system, taken along the line 8-8 from FIG.5 with other items removed for clarity;

[0030]FIG. 9 is a schematic depicting the profiles that may be createdwithin the distal-end region of the catheter of FIG. 5 when the firststeering tendon and the second steering tendon are axially displaced ina proximal direction;

[0031]FIG. 10 is a cross-sectional plan view of the distal-end region ofanother configuration of the catheter of FIG. 1 depicting the attachmentpoints for the steering tendons, wherein the steering tendons aredisposed approximately angularly aligned;

[0032]FIG. 11 is a cross-section view of the distal-end region depictingthe steering tendons disposed approximately angularly aligned on thesame side of the torque transfer system, taken along the line 11-11 fromFIG. 10 with other items removed for clarity;

[0033]FIG. 12 is a schematic depicting the profiles that may be createdwithin the distal-end region of the catheter of FIG. 10 when the firststeeling tendon and the second steering tendon are axially displaced ina proximal direction;

[0034]FIG. 13 is a cross-sectional plan view of the distal-end region ofanother configuration of the catheter of FIG. 1 depicting the secondsteering tendon attached to the inner surface of the support system; and

[0035]FIG. 14 is a schematic depicting the catheter of FIG. 1 in use ina biological cavity within a patient.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Referring now to the drawings, in which like reference numeralsare used to designate like or corresponding elements among the severalfigures, in FIG. 1 there is shown a catheter 20 incorporating aspects ofthe present invention. The catheter 20 includes a sheath 22 having aflexible distal-end region 24, a proximal region 26 and an open lumen 28running throughout. At the distal end 30 of the distal-end region 24 isa distal tip 32. The distal-end region 24 includes a tip electrode 34for applying ablation energy to a biological site. Located proximal fromthe tip electrode 34 are three band electrodes 36 arranged in asubstantially linear array along the distal-end region 24 of the sheath22. The band electrodes 36 are arranged so that there is space 38between adjacent electrodes. In one configuration, the band electrodes36 are two mm wide and the space 38 between the electrodes is also twomm wide. Alternatively, the band electrodes 36 may be three mm wide andthe space 38 between the electrodes may be four mm wide, or any otherdimensions suitable for mapping and/or ablation procedures. The bandelectrodes 36 may be used to map the interior surfaces of the heart orto apply ablation energy, or both. The tip electrode 34 may be used todeliver RF energy to the biological site to form spot or tip-draglesions, or for mapping, or for both. Individual lead wires 40 (notshown in FIG. 1) run from the handle 42 to each band electrode 36.

[0037] With reference to FIG. 2, which is a cross-sectional view takenfrom FIG. 1, the proximal region 26 of the sheath 22 is a layeredcomposite. The inner layer 44 is a hollow tube made of a polymerpossessing a high modulus of elasticity, such as polyetheretherketone(PEEK). A middle layer 46 having one or more layers of braided, 0.025mm×0.075 mm stainless steel ribbons is applied upon the inner layer 44to increase the torque transfer strength of the proximal region 26. Onlyone layer is shown in FIG. 2 for clarity of illustration. The proximalregion's 26 outer layer 48 is made of a flexible, intermediate-durometerpolymer such as polyether block amide, known commercially as Pebax™. Inone embodiment, the outer layer 48 includes a 63D (Shore “D” hardnessscale) hardness scale Pebax™ tube. The three layers 44, 46, and 48 arebonded together by the simultaneous application of heat and pressure,thus creating a flexible tube with the braided stainless steel ribbonsof the middle layer 46 providing superior torsional rigidity.

[0038] With reference to FIG. 3, which is a cross-sectional view takenfrom FIG. 1, the construction of the distal-end region 24 includes asingle layer 50 of a lower durometer Pebax™. In one embodiment, thelayer 50 includes a 35D (Shore “D” hardness scale) hardness scale Pebax™tube. Accordingly, the distal-end region 24 is more flexible and haslower torque transfer strength than the proximal region 26. To furtherincrease flexibility, the distal-end region 24 of the sheath 22 may havea lower durometer material or a thinner wall.

[0039] Referring to FIG. 4, the distal ends of the three layers 44, 46and 48 are stepped, thus exposing the outer surface of the inner layerand the braided stainless steel ribbons of the middle layer. A proximalportion of the distal-end region 24 of the sheath 22 overlaps theexposed portion of the middle layer 46 of the proximal region 26 andbutts against the distal end of the outer layer 48 of the proximalregion. The proximal portion of the distal-end region 24 is then bondedto the distal portion of the proximal region 26 to form one continuoussheath 22 through techniques that are well known to those skilled in theart, such as with epoxy. The proximal end 52 of the sheath 22 is bondedto the handle 42 (FIG. 1), such as with cyanoacrylate adhesive, orattached by some equivalent mechanical means.

[0040] With continuing reference to FIG. 4, the tip electrode 34includes a substantially dome-shaped distal portion 54 and asubstantially cylindrical proximal portion 56. The two portions 54, 56are contiguous and are preferably formed as a single unitary structure.The tip electrode 34 includes a bore 58 that penetrates the proximalsurface 60 of the proximal portion 56. The proximal portion 56 alsoincludes raised ridges 62 to aid in anchoring the tip electrode 34 tothe sheath 22. The tip electrode 34 is formed from a biocompatiblematerial having high thermal conductivity properties. Possible materialsinclude silver, gold, chromium, aluminum, molybdenum, tungsten, nickel,platinum, and platinum/10% iridium.

[0041] With reference to FIG. 5, lead wires 40 are attached to the bandelectrodes 36 in a way that establishes good electrical contact, such asby welding. The lead wires 40 are grouped together and enclosed within asheath 64 that spans throughout the distal-end region 24 and continuesinto the proximal region 26 of the sheath 22. The sheath 64 is formed ofa flexible material, such as a thin-walled heat-shrink tubing, so thatit may deflect when needed.

[0042] With further reference to FIG. 5, a pair of thermocouple wires 66run from the handle 42 shown in FIG. 1 through the sheath 22 to the bore58 within the tip electrode 34. Each of the thermocouple wires 66 isindividually attached at the distal end of the bore 58 in the tipelectrode 34 in a way that achieves good electrical contact, such as bysoldering. By attaching the thermocouple wires 66 to the tip electrode34 in this manner, the thermocouple effect is achieved through the tipelectrode, and good thermal contact is achieved for a more accuratedetermination of the temperature of the tip electrode. After beingattached to the bore 58, the thermocouple wires 66 are potted into thebore with a resin 68, such as epoxy. One of the thermocouple wires 66also serves as a drive wire to transmit ablation energy to the tipelectrode 34. Exemplary configurations of electrodes having combinationthermocouple/drive wires are disclosed in U.S. Pat. Nos. 6,049,737 and6,045,550. The thermocouple wires 66 are grouped together and enclosedwithin a sheath 70 that spans throughout the distal-end region 24 andcontinues into the proximal region 26 of the sheath 22. The sheath 70 isformed of a flexible material, such as a thin-walled heat-shrink tubing,so that it may deflect when needed. In an alternate embodiment, thethermocouple wires are twisted and soldered together prior to beingsoldered into the tip electrode. While the thermocouple effect in thisconfiguration does not depend on the tip electrode, the attachment ofthe thermocouple to the tip electrode does provide the wire pair withgood thermal contact.

[0043] Referring again to FIG. 4 and to FIG. 6, a torque transfer systemthat includes an eyelet 72 and a flat ribbon 74 is housed within thesheath 22. The torque transfer system is adapted to increase the torquetransfer strength of the distal-end region 24 and to facilitate thetransfer of torsional forces from the proximal region 26 of the sheath22 to the distal-end region 24 of the sheath. The eyelet 72 is tubularin shape and includes a central lumen 76. A proximal end 78 of theeyelet 72 includes an enlarged, non-circular flange 80 with asubstantially angular shape, such as a hexagon. The non-circular flange80 has a cross-sectional diameter that is greater than the innerdiameter of the sheath 22. Near the distal end 82 of the eyelet 72 is acircular flange 84 that protrudes outwardly. Extending through thedistal end 82 of the eyelet 72 is a pair of longitudinal, diametricallyopposed slots 86. The eyelet 72 is preferably made from a metallicmaterial, such as stainless steel. The eyelet 72 is installed into thecentral lumen 28 of the sheath 22, prior to the joining of thedistal-end region 24 and the proximal region 26, by inserting theproximal end 78 of the eyelet into the distal end 90 of the proximalregion of the sheath until the circular flange 84 butts against thedistal end of the proximal region. Such installation secures thenoncircular flange 80 of the eyelet 72 within the sheath 22 by embeddingitself into the inner surface 92 of the proximal region 26 of thesheath.

[0044] With continued reference to FIGS. 4 and 6, the flat ribbon 74includes a distal end 94 and a proximal end 96, and is preferably madefrom a resiliently deformable, shape-memory material, such as Nitinol.Such material permits the flat ribbon 74 to deflect with the distal-endregion 24 of the sheath 22, yet the shape-memory aspect of the flatribbon tends to return the flat ribbon, and also the catheter distalend, to the straight, or non-deflected, shape as shown in FIGS. 5 and10. In one embodiment, the flat ribbon 74 includes a flattened Nitinolwire and has a substantially rectangular cross section with a width thatis substantially greater than its thickness. In this way, the flatribbon 74 bends most easily in the direction of its smallest bendingstiffness, which is in a direction perpendicular to its width. Thedistal end 94 of the flat ribbon 74 is attached to the distal-end region24 of the sheath 22 and the proximal end 96 of the flat ribbon isattached to the proximal region 26 of the sheath. More specifically, theproximal end 96 of the flat ribbon 74 is installed through the distalend 30 of the distal-end region 24, inserted into the slots 86 withinthe eyelet 72, and bonded into place, such as with epoxy, or attached byan equivalent mechanical means. Further, lateral movement of theproximal end 96 of the flat ribbon 74 is restricted by the inner surface92 of the sheath 22. The distal end 94 of the flat ribbon 74 isinstalled into the bore 58 of the distal tip 32 and is bonded into placewith the resin 68. In this fashion, the flat ribbon 74 bridges theentire distal-end region 24 between the proximal region 26 and thedistal tip 32. Such installation positions the flat ribbon 74 along thecenterline 98 of the distal-end region 24 of the sheath 22.

[0045] The torsional rigidity of the distal-end region 24 issignificantly enhanced by the installation of the flat ribbon 74. As aresult, rotations of the handle 42 (FIG. 1) by the operator areaccurately transferred to the distal tip 32. More specifically, as thehandle 42 is rotated, the torsional forces that are exerted transfer tothe proximal region 26 of the sheath 22 because of the attachment meansbetween the handle and the sheath. The braided stainless steel ribbonsof the middle layer 46 (FIGS. 2 and 4) within the proximal region 26transfers the torsional forces to the distal end 90 of the proximalregion of the sheath 22. The torsional forces are then transferred tothe eyelet 72 (FIGS. 4 and 6) by means of the non-circular flange 80that is embedded within the distal end 90 of the proximal region 26.Since the embedded portion of the eyelet 72 is non-circular, the eyeletwill not rotate freely within the proximal region 26 of the sheath 22.Therefore, the torsional forces are transferred from the eyelet 72 tothe flat ribbon 74 (FIGS. 4 and 6) whose proximal end 96 is interrelatedwith the slots 86 in the eyelet. Since the distal end 94 of the flatribbon 74 is bonded into the bore 58 of the distal tip 32 (FIG. 4), thetorsional forces are transferred to the distal tip. With the enhanceddistal torque transfer provided by the flat ribbon 74, the torqueimparted by the proximal region 26 is effectively transferred to thedistal tip 32 without the need for a middle layer of braided materialwithin the distal-end region 24, such as the middle layer 46 of theproximal region. As is well known, additional layers increase stiffness,size, and cost. A significant advantage of the torque transfer systemusing the flat ribbon 74 is that rotational handle 42 movements will beaccurately transferred to the distal tip 32. Thus, the operator canplace the distal tip 32 of the catheter 20 at a desired location withina patient with greater precision and the possibility of harm to thepatient due to an uncontrolled “whipping” type movement of the distalregion is sharply reduced. Another advantage of having the flat ribbon74 within the distal-end region 24 is that by rotating the handle 42with the distal-end region in the deflected condition, the distal tip 32can exert a relatively great amount of force against the desiredlocation.

[0046] With continued reference to FIG. 4, housed within the sheath 22is a first steering tendon 100 and a second steering tendon 102. Thedistal end 104 of the first steering tendon 100 is offset from thelongitudinal centerline 98 of the sheath 22. In order to applydeflection force directly to the distal tip, the distal end 104 of thefirst steering tendon 100 is inserted into the bore 58 of the distal tip32. The distal end 104 is then bonded into place with the resin 68. Aswill be discussed below in more detail, by placing the distal end 104 ofthe first steering tendon 100 at a location offset from the longitudinalcenterline 98 of the sheath 22 and therefore proximate the inner surface92 of the sheath 22, a relatively low amount of force applied to thefirst steering tendon 100 will generate a bending moment sufficient todeflect the distal-end region 24. To ensure a good bond between theresin 68 and the first steering tendon 100, and good anchoring of thetendon within the tip electrode, the distal end 104 of the firststeering tendon is hook-shaped with a ball 106 disposed at the end. Aswill be discussed below in more detail, the distal end 108 (see FIGS. 4,5, 10 and 13) of the second steering tendon 102 is attached within thedistal-end region 24, proximate the inner surface 92 of the sheath 22,and proximal the attachment point of the first steering tendon 100. Withreference to FIG. 1, the proximal end 110 of the first steering tendon100 and the proximal end 112 of the second steering tendon 102 exitthrough the proximal end 52 of the sheath 22, and attach to a steeringcontroller 114 within the handle 42. For clarification purposes, infollowing discussions, the term “attachment point” in relation to thedistal end 104 of the first steering tendon 100 refers to the distal endof the first steering tendon being secured within the distal tip 32.

[0047] In some catheters that have a flat ribbon within the distal-endregion and a steering tendon attached to a point proximal the distal tipwithin the distal-end region, undesirable deformation of the sheath canoccur when the steering tendon is axially displaced in the proximaldirection. More specifically, as the steering tendon is axiallydisplaced in the proximal direction, the flat ribbon reduces the amountof axial displacement that the distal tip would normally experience. Asa result, the portion of the sheath in the distal-end region proximalthe attachment point compresses, thus causing that region of the sheathto wrinkle, and the portion of the sheath distal the attachment pointstretches. Such deformation of the sheath can lead to fluid ingressbeneath the catheter's band electrodes or can cause damage to internalwires or mechanical components. To reduce deformation of the sheath, thepresent catheter 20 includes a support system or compression cage 116(FIGS. 4, 5, 10 and 13) within the distal-end region. The support system116 functions to prevent the axial compression of the sheath 22 in thedistal-end region 24 in the area proximal the attachment point of thesecond steering tendon 102, while still permitting deflection in thesteering direction within that region. The prevention of axialcompression in the distal-end region 24 in the area proximal theattachment point of the second steering tendon 102 coincidentallyprevents the stretching of the distal-end region in the area distal theattachment point of the second steering tendon.

[0048] As shown in FIG. 4, the support system 116 includes a proximalend 118, a distal end 120, and a central lumen 122 there between. Thesupport system 116 is preferably made from a resilient material, such asNitinol, spring-temper austenitic stainless steel, or heat-treatablestainless steel so that it tends to return to a pre-established shape,such as straight. The proximal end 118 of the support system 116 isbonded to the distal end 82 of the eyelet 72, such as with epoxy. In oneembodiment, an anchor band 124 (discussed in more detail below) isbonded to the distal end 120 of the support system 116 (FIGS. 4, 6 and10), such as with epoxy. The flat ribbon 74 and tendons 100,102 arehoused within the support system.

[0049] With reference to FIGS. 7A-7E, various configurations of thesupport system or compression cage 116 are shown. In one configuration(FIG. 7A), the compression cage 116 includes a flat-wire coil 126 andtwo substantially longitudinal struts 128. The struts 128 arediametrically opposed from each other and are welded, soldered, brazed,adhered, or otherwise attached to some or all loops of the coil 126. Inanother configuration (FIG. 7B), the compression cage includes around-wire coil 130 and two substantially longitudinal struts 132. Thestruts 132 are diametrically opposed from each other and are welded,soldered, brazed, adhered, or otherwise attached to some or all loops ofthe coil 130. In another configuration (FIGS. 7C and 7D), thecompression cage includes a substantially tubular member 134 with anarray of deep notches 136 that are diametrically opposed from eachother. The material remaining between opposing notches 136 function asstruts 138. In yet another configuration (FIG. 7E), the compression cageincludes a linear array of rings 140 and two substantially longitudinalstruts 142 that interconnect the rings. The struts 142 are diametricallyopposed from each other and are welded, soldered, brazed, adhered, orotherwise attached to each of the rings 140.

[0050] The primary function of the struts 128, 132, 138, 142 is toprovide columnar strength to the compression cage 116. When a tensileload is applied to a steering tendon 100,102 to induce deflection of thedistal-end region 24, the reaction to the load is carried by the struts128, 132, 138, 142 within the compression cage 116 and transferred viathe eyelet 72 into the relatively rigid proximal region 26. Thecompression cage deflects laterally most easily in a direction that isperpendicular to the plane in which a pair of opposing struts 128, 132,138, 142 are located.

[0051] The support system 116 and anchor band 124 are independent of,but reside within, the central lumen 122 of the sheath 22 of thedistal-end region 24. More specifically, the support system and anchorband are not attached directly to the sheath 22 of the distal-end region24. In this configuration, a tensile load produced by axial translationof the second steering tendon 102 in the proximal direction causes thesupport system 116 and anchor band 124 to deflect laterally and pushagainst the distal-end region 24, thereby causing the distal-end regionto deflect. With the support system 116 and anchor band 124 beingindependent of the distal-end region 24 of the sheath 22, they do notcause the distal-end region to be either compressed or stretched.

[0052] In an alternate configuration, the support system 116 and anchorband 124 are attached to the inner surface 92 of the sheath 22 withinthe distal-end region 24, such as by melt-bonding, adhesives, or someequivalent mechanical means. As a result, a tensile load produced byaxial translation of the second steering tendon 102 in the proximaldirection causes the distal-end region 24 to compress in the area of thesupport system and to stretch in the area distal the support system.However, as previously mentioned, the reaction to the tensile load iscarried by the struts 128, 132, 138, 142 within the support system 116and is transferred via the eyelet 72 into the relatively rigid proximalregion 26 of the sheath 22, thereby minimizing the associatedcompression and stretching of the distal-end region 24 of the sheath.

[0053] With reference to FIGS. 5 and 6, the anchor band 124 has twohollow cylindrical sections 143, 145 of different diameters with a step152 between the cylindrical sections. The first cylindrical section 143has a first inner surface 144 and a first outer surface 148, while thesecond cylindrical section 145 has a second inner surface, 146 andsecond outer surface 150. The diameters of the first inner 144 and outer148 surfaces are smaller than the diameters of the second inner 146 andouter 150 surfaces, respectively. The first outer surface 148 isinserted and bonded into the distal end 120 of the support system 116prior to installation within the distal-end region 24. In oneconfiguration, the support system 116 and anchor band 124 are attachedto the inner surface 92 of the sheath 22. In this configuration, thesecond outer surface 150 of the anchor band 124 and the outer surface ofthe support system 116 are roughened, for example, by machining or by amicro-blasting process, in order to improve adhesion properties. Theanchor band 124 is preferably made from a metallic material, such asstainless steel.

[0054] In this embodiment, the anchor band 124 is located proximal themost proximal band electrode 36. The distal end 108 of the secondsteering tendon 102 is welded, soldered, brazed, adhesively bonded, orotherwise attached to the first inner surface 144 of the anchor band124. Such placement puts the distal end 108 of the second steeringtendon 102 at a location offset from the centerline 98 of the sheath 22and proximate the inner surface 92 of the sheath 22. As will bediscussed below in more detail, by placing the distal end 108 of thesecond steering tendon 102 at a location offset from the centerline 98of the sheath 22 and proximate the inner surface 92 of the sheath 22, arelatively low amount of force applied to the second steering tendonwill generate a bending moment sufficient to deflect the distal-endregion 24.

[0055] To attain optimal deflecting performance within the distal-endregion 24, the deflecting direction of the compression cage 116 isparallelly aligned with the deflecting direction of the flat ribbon 74.As previously mentioned, the compression cage 114 deflects laterallymost easily in a direction that is perpendicular to the plane in which apair of opposing struts 128, 132, 138, 142 are located, and the flatribbon 74 deflects most easily in a direction that is perpendicular tothe width of the flat ribbon. A ribbon locator 154 is installed withinthe anchor band 124 (FIGS. 5 and 6) to ensure proper alignment betweenthe pair of opposing struts 128, 132, 138, 142 and the flat ribbon 74during catheter assembly, thereby aligning the easiest deflectingdirection of the flat ribbon with the easiest deflecting direction ofthe support system 116. The ribbon locator 154 is oriented so that theedges 156 on the ribbon locator are parallel to the plane in which thestruts 128, 132, 138, 142 are located and offset from the plane so thatupon installation into the distal-end region 24, the edges 156 on theribbon locator are adjacent to a face 158 on the flat ribbon 74. Theribbon locator 154 is welded, soldered, brazed, adhered, or otherwiseattached to the first inner surface 144 of the anchor band 124. Wheninstalling the anchor band 124 and support system 116 within thedistal-end region 24, the anchor band is oriented so that the edges 156on the ribbon locator 154 are aligned to be parallel with the face 158on the flat ribbon 74 on a side opposite the attachment point of thedistal end 108 of the second steering tendon 102. The anchor band 124and support system 116 are then bonded to the distal-end region 24 tofix the alignment of the flat ribbon 74 relative to the support system.

[0056] With the attachment of the support system 116 to the eyelet 72,torsional forces from the eyelet are transferred to the support system.The torsional forces in the support system are then transferred to thedistal portion 120 of the support system 116 and into the ribbon locator154. With the edges 156 of the ribbon locator 154 positioned adjacent tothe face 158 on the flat ribbon 74, torsional forces from the ribbonlocator are transferred to the flat ribbon, thus enhancing the torquetransfer capabilities of the torque transfer system.

[0057] With reference to FIGS. 4, 5 and 10, a ribbon isolation sleeve160 includes a proximal end 162, a distal end 164, and a central lumen166 there between. The ribbon isolation sleeve 160 is preferably madefrom a tubular-shaped resilient material, such as Pebax™. It is alsopreferable that the ribbon isolation sleeve 160 include a wire coil 167(FIG. 4) embedded therein, such as a stainless steel wire coil. Thepurpose of the ribbon isolation sleeve 160 is twofold: 1) to reducewrinkling of the distal-end region 24 in the area between the anchorband 124 and the distal tip 32 during distal-tip steering, and 2) toreduce the likelihood of a short circuit between the flat ribbon 74 andthe attachment points of the lead wires 40. The ribbon isolation sleeve160 is housed within the distal-end region 24, with its proximal end 162inserted and bonded into the second inner surface 146 of the anchor band124, such as with cyanoacrylate. The lead wires 40 are routed distallythrough the ribbon isolation sleeve 160. The lead wires then wrap aroundthe distal end 164 of the ribbon isolation sleeve 160 and are routedproximally towards the band electrodes 36.

[0058] With continued reference to FIG. 5, the first steering tendon 100and the second steering tendon 102 are both housed within the sheath 22,are offset from the centerline 98 of the sheath, and are locatedproximate the inner surface 92 of the sheath. The first steering tendon100 is attached at a location distal the second steering tendon 102. Thegeneral orientation of the steering tendons in the present embodiment isshown in the cross-sectional view of FIG. 8 where the first steeringtendon 100 is located approximately 180° apart from the second steeringtendon 102, on opposite sides of the flat ribbon 74. As shown in FIG. 9,having the steering tendons 100, 102 attached approximately 180° apartproduces deflection profiles of the distal-end region 24 in oppositedirections on opposite sides of the catheter 20. In this configuration,the catheter 20 steers in different directions when the steering tendons100, 102 are axially displaced, thus the catheter is bidirectional.

[0059] With further reference to FIG. 5, the steering tendons 100, 102may be formed from stainless steel wire having a diameter ofapproximately 0.2 mm. To reduce friction and thereby minimize the forcerequired to steer the catheter 20, the two steering tendons 100, 102 areeach enclosed within a respective sheath 168, 170. The sheaths 168, 170cover substantially the entire length of the steering tendons 100, 102and provide a relatively small clearance to permit the steering tendonsto readily slide within the sheaths 168, 170. The sheaths include atubular, polymeric material and are either coated or are formed of a lowfriction material, such as polytetrafluoroethylene (PTFE), knowncommercially as Teflon™.

[0060] The profile of the distal-end region 24 can be adjusted bymanipulating the steering controller 114 (FIG. 1), which axiallydisplaces either the first steering tendon 100 or the second steeringtendon 102 in the proximal direction. Axially displacing a steeringtendon in the proximal direction causes that steering tendon toexperience greater tension. The tensile load is transferred to thesteering tendon's 100, 102 distal attachment point, where othercomponents of the catheter 20 structure react with a compressive loadessentially equal in magnitude to the tensile load applied by thesteering tendon. The tensile and compressive loads exist within thesteering tendon 100, 102 and certain other components of the catheterstructure, respectively, at all locations that are proximal to thetendon's distal attachment point. In addition, a bending moment is alsopresent because the steering tendon's 100, 102 distal attachment point,by design, does not coincide with the longitudinal axis or centerline 98of the catheter shaft 22.

[0061] More specifically, if tension is applied to the first steeringtendon 100, it carries a tensile load to its distal attachment point,the tip electrode 34. At the attachment point, that tensile load isreacted to by an equivalent compressive load that is carried by severalcomponents within the catheter 20 structure, notably the flat ribbon 74,eyelet 72, and proximal region 26 of the sheath 22. One effect of theessentially equal but opposite axial forces is that the overall lengthof the catheter 20 structure somewhat shortens while the overall lengthof the first steering tendon 100 slightly lengthens. A substantialbending moment is also present at the attachment point because the twoforces are deliberately offset from one another by the distance betweenthe flat ribbon 74 and first steering tendon 100. The bending momentincreases as the distance between the flat ribbon 74 and the firststeering tendon 100 increases. The effect of the bending moment is todeflect the distal tip 32 toward the side to which the first steeringtendon 100 is attached. Such deflection is balanced by the inherentbending stiffness of certain components of the catheter 20 structure,notably the flat ribbon 74, ribbon isolation sleeve 160, support system116, and the distal-end region 24 of the sheath 22. As more tension isapplied to the first steering tendon 100, the bending moment increasesand thereby causes further deflection of the resisting components.Ultimately, the deflected shape 172 of the catheter's distal endresembles a circle (FIG. 9).

[0062] If tension is applied to the second steering tendon 102, itcarries a tensile load to its distal attachment point, the anchor band124. The tensile load at the attachment point is reacted to by anequivalent compressive load that is carried primarily by the supportsystem 116, eyelet 74, and proximal region 26 of the sheath 22. Theoverall length of the compressive load carrying elements somewhatshortens while the overall length of the second steering tendon 102somewhat lengthens. A substantial bending moment is generated at thesecond steering tendon's 102 distal attachment point, and its effect isto deflect the anchor band 124 toward the side to which the secondsteering tendon is attached. The deflection is balanced by the inherentbending stiffness of certain components of the catheter 20 structure,notably the support system 116, a portion of the flat ribbon 74, and thedistal-end region 24 of the sheath 22. The ribbon isolation sleeve 160and the distal portion of the flat ribbon 74 remain straight because thebending moment arises at the anchor band 124, which is located proximalthe ribbon isolation sleeve. As more tension is applied to the secondsteering tendon 102, the resulting bending movement increases andthereby causes further deflection of the resisting components.Ultimately, the deflected shape 174 of the catheter's distal endresembles a letter “U” (FIG. 9).

[0063] The bending or deflection profiles 172, 174 (FIG. 9) of thecatheter are somewhat asymmetric, a result of the axial displacementbetween the distal end mounting locations of the steering tendons 100,102. The degree of difference in the deflection profiles 102, 104depends upon the location of the attachment point of the distal end 108of the second steering tendon 102 in comparison to the first steeringtendon 100. Thus, the steering profiles can be altered by changing thelocation of the attachment point of the distal end 108 of the secondsteering tendon 102.

[0064] The components within the catheter that experience steeringdeflection are designed accordingly. For example, the flat ribbon 74 isrelatively wide and thin and made of a highly resilient material so itwill easily bend in one plane and will recover elastically after extremedeflection. Similarly, the steering tendons 100, 102 possess a smalldiameter and are made of spring temper stainless steel. The supportsystem 116, in a preferred embodiment, is slotted such that it mayreadily accommodate bending in a specific plane, and the slot pattern ispurposely helical to provide additional stability during extremedeflections. Furthermore, the external dimensions of both the supportsystem 116 and the ribbon isolation sleeve 160 serve to substantiallyfill the distal-end region 24 of the sheath 22 to prevent it frombuckling or otherwise experiencing nonuniform deformation during extremesteering deflections.

[0065] Although not shown, in an alternative configuration the distalends 104, 108 of the steering tendons 100, 102 may both be attached tothe distal tip 32 or to the proximal anchor band 124 such that thepoints of attachment are 1) axially identical along the length of thesheath and 2) angularly displaced from each other along thecircumference of the inner surface of the sheath. Such placement of thesteering tendons 100, 102 causes the deflection profiles of the catheter20 to be identical although they will be angularly displaced from eachother. For example, when the distal ends 104, 108 of the steeringtendons 100, 102 are attached approximately 1800 apart along the innersurface 92 of the sheath 22 as shown in FIG. 8, but are attached suchthat the distal ends are located at the same axial distance from thesteering controller 114, the deflections will be symmetric and occur inopposite directions.

[0066] With reference to FIG. 10, an alternative embodiment of thecatheter of FIG. 1 is depicted wherein both steering tendons 100, 102are approximately angularly aligned on the same side of the flat ribbon74. The first steering tendon 100 is attached at a location distal tothat of the second steering tendon 102. The general orientation of thetendons 100, 102 is shown in the cross-sectional view of FIG. 11 wherethe first steering tendon 100 is located closer to the longitudinalcenterline 98 of the catheter sheath 22 than the second steering tendon102. As shown in FIG. 12, having the steering tendons 100, 102approximately angularly aligned produces different deflection profileson the same side of the catheter. In this configuration, the catheter 20steers in the same direction when either steering tendon 100, 102 isaxially displaced, thus the catheter deflection is unidirectional andasymmetric. However, the attachment of the first steering tendon 100 tothe catheter sheath 22 at a position distal the second steering tendon102 permits a greater curl to the deflected distal end, as shown in FIG.12. The first dashed profile 172 is achieved through axial movement ofthe first steering tendon 100 alone while the second dashed profile 174is achieved through axial movement of the second steering tendon 102alone.

[0067] In FIG. 13, another embodiment is depicted where the anchor band124 is removed and the distal end 108 of the second steering tendon 102is welded, soldered, brazed, adhered, or otherwise attached directly tothe inside surface 122 at the distal end 120 of the support system 116.Furthermore, the ribbon isolation sleeve 160 is bonded to the distal end120 of the support system 116. In one embodiment, the support system 116is independent of, but resides within, the central lumen 122 of thesheath 22 of the distal-end region 24. More specifically, the supportsystem is not attached directly to the sheath 22 of the distal-endregion 24. In this configuration, a tensile load produced by axialtranslation of the second steering tendon 102 in the proximal directioncauses the support system 116 to deflect laterally and push against thedistal-end region 24, thereby causing the distal-end region to deflect.With the support system 116 being independent of the distal-end region24 of the sheath 22, it does not cause the distal-end region to beeither compressed or stretched. In an alternate configuration, thesupport system 116 is attached to the inner surface 92 of the sheath 22within the distal-end region 24, such as by melt-bonding, adhesives, orsome equivalent mechanical means. As a result, a tensile load producedby axial translation of the second steering tendon 102 in the proximaldirection causes the distal-end region 24 to compress in the area of thesupport system and to stretch in the area distal the support system.However, as previously mentioned, the reaction to the tensile load iscarried by the struts 128, 132, 138, 142 within the support system 116and is transferred via the eyelet 72 into the relatively rigid proximalregion 26 of the sheath 22, thereby minimizing the associatedcompression and stretching of the distal-end region 24 of the sheath.

[0068] As shown in FIG. 13, in an alternative embodiment where theanchor band is not used, the ribbon locator 154 is welded, soldered,brazed, adhered, or otherwise attached to the inner surface 122 of thesupport system 116. The ribbon locator 154 is positioned so that theedges 156 of the ribbon locator are parallel to the pair of opposingstruts 128, 132, 142, 138 (FIGS. 7A-7E). When installing the supportsystem 116 within the distal-end region 24, the support system isoriented so that the edges 156 of the ribbon locator 154 are aligned tobe parallel with the face 158 on the flat ribbon 74 on a side oppositethe attachment point of the distal end 108 of the second steering tendon102, and then bonded to the eyelet 72.

[0069] With reference to FIG. 14, in operation, a catheter 20 havingbidirectional deflection configured in accordance with the invention isintroduced into a biological site 176, such as the right atrium of theheart. During introduction, the catheter 20 is maintained in asubstantially linear arrangement 178. While the distal end region 24 ofthe catheter 20 is being positioned near the area of target tissue 180to be ablated, the distal-end region is deflected by pulling on theappropriate one of the steering tendons 100, 102, as previouslydescribed. Once the distal-end region 24 is adequately deflected 182 toestablish contact between the tip electrode 34 and the area of targettissue 180, ablation energy is applied through the tip electrode. If thetarget tissue 180 comprises a linear segment, the catheter 20 is pulledin the proximal direction during the application of ablation energy toproduce a lesion having length, as opposed to only a spot lesion.

[0070] Because the location of the attachment point of the firststeering tendon 100 to the catheter sheath 22 is more distal than thatof the second steering tendon 102 (see FIGS. 5 and 10), for an equaldistance of axial translation of the steering tendons the firstdeflection profile 172 (see FIGS. 9 and 12) does not move the tipelectrode 34 as far from the centerline 98 of a non-deflected catheteras does the second deflection profile 174. Also, the first deflectionprofile 172 may permit more force to be applied to the target site.Therefore, referring to FIG. 14, in instances where the target tissue180 is located within a compact cavity within the patient, or arelatively higher amount of force is to be applied to the target tissue,it may be desirable to utilize the first deflection profile 172 of thecatheter 20. Conversely, where the target tissue 180 is located within amore open cavity within the patient, or a relatively lower amount offorce is to be applied to the target tissue, it may be desirable toutilize the second deflection profile 174 of the catheter 20. Hence,because of its ability to be configured with different distal enddeflection profiles 172, 174, the catheter 20 of the present inventionmay be used to form multiple lesions in different environments within apatient without the need of multiple catheters.

[0071] It will be apparent from the foregoing that, while particularforms of the invention have been illustrated and described, variousmodifications can be made without departing from the spirit and scope ofthe invention. For instance, the present invention describes a steerablecatheter that comprises two steering tendons. However, the torquetransfer system and support system described herein can also be appliedto catheters with only one steering tendon or more than two steeringtendons.

What is claimed is:
 1. A method of delivering therapeutic treatment to abiological site, comprising: providing a catheter having, a sheathincluding a proximal region, a distal-end region, and longitudinalcenterline, a support system having a proximal end, a distal end and alumen there between, the support system sized to fit within thedistal-end region of the sheath and configured to deflect laterallyrelative to the centerline and to resist axial compression along thecenterline, and a torque transfer system housed within the compressioncage and adapted to transfer torsional forces from the proximal regionof the sheath to the distal-end region of the sheath; manipulating thedistal end region of the catheter until the distal-end region of thecatheter is proximate the biological site; and providing therapeutictreatment to the biological site.
 2. The method of claim 1, whereinproviding a catheter having a support system includes providing acatheter having a support system including a helical coil defining thelumen and at least one strut secured to one side of the coil throughoutthe length of the coil.
 3. The method of claim 2, wherein providing acatheter having a support system including a helical coil and at leastone strut secured to one side of the coil throughout the length of thecoil includes providing a catheter having a support system including apair of struts secured to diametrically opposite sides of the coil. 4.The method of claim 2, wherein providing a catheter having a supportsystem including a helical coil and at least one strut secured to oneside of the coil throughout the length of the coil includes providing acatheter having a support system which is formed of a resilientlydeformable, shape-memory material.
 5. The method of claim 1, whereinproviding a catheter having a support system includes providing acatheter having a support system including a linear array of hollowrings defining the lumen and at least one strut secured to one side ofeach of the rings.
 6. The method of claim 5, wherein providing acatheter having a support system including a linear array of hollowrings and at least one strut secured to one side of each of the ringsincludes providing a catheter having a support system including a pairof struts secured to diametrically opposite sides of each of the rings.7. The method of claim 5, wherein providing a catheter having a supportsystem including a linear array of hollow rings and at least one strutsecured to one side of each of the rings includes providing a catheterhaving a support system which is formed of a resiliently deformable,shape-memory material.
 8. The method of claim 1, wherein providing acatheter includes providing a catheter having at least one steeringtendon housed within the sheath, the steering tendon having a first endattached to the distal-end region of the sheath, and a second endlocated at the proximal region of the sheath.
 9. The method of claim 8,wherein manipulating the distal-end region of the catheter includespulling the at least one steering tendon in a proximal direction tocause the sheath distal-end region to deflect.
 10. The method of claim1, wherein: providing a catheter includes providing a catheter having ahandle coupled to the proximal end of the sheath; and manipulating thedistal-end region of the catheter includes rotating the handle.
 11. Amethod of delivering therapeutic treatment to a biological site,comprising: providing a catheter having, a sheath including a proximalregion, a distal-end region, and a longitudinal centerline, and asupport system having a helical coil defining a proximal end, a distalend, a lumen there between and at least one strut secured to one side ofthe coil throughout the length of the coil, the support system sized tofit within the distal-end region of the sheath and configured to deflectlaterally relative to the centerline and to resist axial compressionalong the centerline; manipulating the distal end region of the catheteruntil the distal-end region of the catheter is proximate the biologicalsite; and providing therapeutic treatment to the biological site. 12.The method of claim 11, wherein providing a catheter having a supportsystem including a helical coil and at least one strut secured to oneside of the coil throughout the length of the coil includes providing acatheter having a support system including a pair of struts secured todiametrically opposite sides of the coil.
 13. The method of claim 11,wherein providing a catheter having a support system including a helicalcoil and at least one strut secured to one side of the coil throughoutthe length of the coil includes providing a catheter having a supportsystem which is formed of a resiliently deformable, shape-memorymaterial.
 14. The method of claim 11, wherein: providing a catheterincludes providing a catheter having at least one steering tendon housedwithin the sheath, the steering tendon having a first end attached tothe distal-end region of the sheath, and a second end located at theproximal region of the sheath; and manipulating the distal-end region ofthe catheter includes pulling the at least one steering tendon in aproximal direction to cause the sheath distal-end region to deflect. 15.The method of claim 11, wherein: providing a catheter includes providinga catheter having a handle coupled to the proximal end of the sheath;and manipulating the distal-end region of the catheter includes rotatingthe handle.
 16. A method of delivering therapeutic treatment to abiological site, comprising: providing a catheter having, a sheathincluding a proximal region, a distal-end region, and a longitudinalcenterline, and a support system having a linear array of hollow ringsdefining a proximal end, a distal end, a lumen there between and atleast one strut secured to one side of each of the rings, the supportsystem sized to fit within the distal-end region of the sheath andconfigured to deflect laterally relative to the centerline and to resistaxial compression along the centerline; manipulating the distal endregion of the catheter until the distal-end region of the catheter isproximate the biological site; and providing therapeutic treatment tothe biological site.
 17. The method of claim 16, wherein providing acatheter having a support system including a linear array of hollowrings and at least one strut secured to one side of each of the ringsincludes providing a catheter having a support system including a pairof struts secured to diametrically opposite sides of each of the rings.18. The method of claim 16, wherein providing a catheter having asupport system including a linear array of hollow rings and at least onestrut secured to one side of each of the rings includes providing acatheter having a support system which is formed of a resilientlydeformable, shape-memory material.
 19. The method of claim 16, wherein:providing a catheter includes providing a catheter having at least onesteering tendon housed within the sheath, the steering tendon having afirst end attached to the distal-end region of the sheath, and a secondend located at the proximal region of the sheath; and manipulating thedistal-end region of the catheter includes pulling the at least onesteering tendon in a proximal direction to cause the sheath distal-endregion to deflect.
 20. The method of claim 16, wherein: providing acatheter includes providing a catheter having a handle coupled to theproximal end of the sheath; and manipulating the distal-end region ofthe catheter includes rotating the handle.
 21. A catheter comprising: asheath including a proximal region, a distal-end region, and alongitudinal centerline; and a support system having a proximal end, adistal end and a lumen there between, the support system sized to fitwithin the distal-end region of the sheath and configured to deflectlaterally relative to the centerline and to resist axial compressionalong the centerline; wherein the support system comprises a helicalcoil defining the lumen and at least one strut secured to one side ofthe coil throughout the length of the coil.
 22. A catheter comprising: asheath including a proximal region, a distal-end region, and alongitudinal centerline; and a support system having a proximal end, adistal end and a lumen there between, the support system sized to fitwithin the distal-end region of the sheath and configured to deflectlaterally relative to the centerline and to resist axial compressionalong the centerline; wherein the support system comprises a lineararray of hollow rings defining the lumen and at least one strut securedto one side of each of the rings.
 23. A catheter comprising: a sheathincluding a proximal region, a distal-end region, and a longitudinalcenterline; a support system having a proximal end, a distal end and alumen there between, the support system sized to fit within thedistal-end region of the sheath and configured to deflect laterallyrelative to the centerline and to resist axial compression along thecenterline; and a ribbon isolation sleeve having a proximal end coupledto the distal-end of the support system.